Climate legislation unveiled Tuesday in the US House of Representatives was welcomed as a "very strong start" by green groups on the sidelines of UN climate talks here.

The draft law presented by Congressman Henry Waxman, chairman of the House Committee on Energy and Commerce will inevitably undergo revision as it wends through the American legislative process.

But it was seen in Bonn as an encouraging sign that Congress would back President Barack Obama's ambitious goals for slashing greenhouse gases, an essential cornerstone for any new global climate treaty.

More than 190 nations in the UN Framework Convention on Climate Change (UNFCCC) have set themselves the task of hammering out an accord in Copenhagen in December.

"The bill is clearly sending a signal to the international community that the US is ready to engage," said Keya Chatterjee, deputy director of the WWF's climate program in the United States.

"You can see that they are doing what they can to empower Obama to negotiate in Copenhagen, to give him the best cards to play with."

The proposed legislation lays out targets for reducing global warming pollution that are even more ambitious than those promised by Obama during his presidential campaign.

Using 2005 levels as a benchmark, it calls for a cut of three percent by 2012, 20 percent by 2020, 42 percent by 2030 and 83 percent by 2050.

The bill would commit the US to an additional 10 percent reduction by funding forest protection programs in tropical countries with the proceeds from a carbon trading market.

Ongoing deforestation -- primarily in Brazil and Indonesia -- accounts for fully 20 percent of annual greenhouse gas emissions.

"This draft, which sets firm limits on the amount of greenhouse gas emissions and makes investments in clean energy and jobs, sends an important signal both domestically and abroad," said Jonathan Lash, president of the World Resources Institute."

Martin Kaiser, a climate expert from Greenpeace International, welcomed the bill as a "first step', but said it contained serious shortfalls.

The Waxman bill "proposes a seven-to-eight percent emission cut on 1990 levels by 2020, going further than the target previously announced by the US administration. However, it doesn't go as far as the science demands or the world needs," he said in a statement.

The European Union (EU) has taken the lead on reducing carbon pollution, promising to slash emissions by 20 percent compared to 1990 levels by 2020, and by 30 percent if other industrialised countries follow suit.

By 2050, it will deepen the cuts to 80 percent.

Environmental Defense Fund President Fred Krupp said the bill "focused on exactly the right issues to quickly build consensus and allow Congress to pass a strong bill this year."